1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly to an apparatus for fabricating apparatus of a flat panel display device, and apparatus and method for detecting a quantity of static electricity thereof.
2. Description of the Related Art
In today's information society, importance of a display device increases as information communication becomes more visual. A cathode ray tube (CRT) or Braun tube was the typical display up until recently. The CRT is heavy and big. In contrast, flat panel display devices are relatively light and have a thin profile. Such flat panel display devices include liquid crystal display (LCD), field emission display (FED) and organic light emitting diode (OLED) devices. These flat panel display devices are now on the market and practical to use.
Among these flat panel devices, the liquid crystal display device has low power consumption, high response speed and the capacity to be manufactured with a very large screen size. The liquid crystal display can be mass produced with a large size display or with a small size display. Thus, the liquid crystal display has been replacing the CRT in many applications.
Generally, a liquid crystal display device controls the light transmittance of liquid crystal cells that are arranged in a matrix shape on a liquid crystal display panel by adjusting a video data signal supplied thereto, thereby displaying a picture on the panel corresponding to the data signal. Further, the liquid crystal display device includes a lower substrate on which electrodes are formed, a thin film transistor on the lower substrate for switching the data signal for each of the electrodes of the liquid crystal cells, a data line on the lower substrate for supplying the data signal supplied from the outside to the liquid crystal cells and a control line on the lower substrate for supplying a control signal to the thin film transistor; an upper substrate on which a color filter is formed; a spacer between the upper and lower substrates to maintain a fixed cell gap between the upper and lower substrates; and a layer of liquid crystal molecules between the upper and lower substrates.
In a fabricating method of a the liquid crystal display device, an active layer having a channel part of the thin film transistor and a passivation film for protecting the thin film transistor are typically formed by use of PECVD (plasma enhanced chemical vapor deposition). FIG. 1 is a cross-sectional view of a fabricating apparatus used in a vacuum deposition process of the related art. The PECVD process forms the liquid crystal display device in the fabricating apparatus shown in FIG. 1.
The fabricating apparatus shown in FIG. 1 includes a process chamber 2 in which a deposition process is performed, and a susceptor 10 that applies heat to a substrate 4 within the process chamber 2 and is used as a lower electrode for generating plasma. Lift pins 6 are installed in the susceptor 10 for lifting the substrate 4. The substrate 4 is transferred onto the susceptor 10 by a robotic arm (not shown) and removed by the robotic arm after the deposition process. The susceptor 10 is fixed to a supporting stand 20. More specifically, the susceptor 10 is positioned within the process chamber 2 at a designated height by the supporting stand 20. The susceptor 10 can be repositioned in a vertical direction within the process chamber 2 by a timing belt (not shown) connected to the supporting stand 20.
The timing belt is driven by a motor (not shown) to move the supporting stand 20 a desired distance or mark, thereby making the susceptor 10 move to a position within the process chamber 2 corresponding to a distance or mark that the supporting stand 20 is at. Accordingly, the fabricating apparatus with such a configuration makes the susceptor 10 on which the substrate 4 is loaded rises to a position where the deposition process can be performed, and applies heat and voltage to the substrate 4 such that a thin film can be deposited with a gas and plasma.
FIG. 2A is a cross-sectional view of a bent substrate because of static electricity generated after a vacuum deposition process. In a plasma deposition process, a large static charge can be created between the substrate 4 and the susceptor 10 by an RF (radio frequency) discharge used to create plasma. The charge (static electricity) causes the substrate 4 to stick or to be attracted to the susceptor 10. Accordingly, as shown in FIG. 2A, a problem is created in the middle part of the substrate 44 where no lift pins are located when the lift pins 46 are deployed by the lowering of the susceptor 10 so that the robot arm (not shown) can pick up the substrate 44. The static electricity retains the center portion of the substrate 44 against the susceptor 50 while the lift pins 46 deploy up as the susceptor 10 lowers so that the substrate 44 is bent. Because the substrate 44 is bent, the robot arm may not be able to get under the bent substrate 44 and may break the bent substrate 44 in trying to do so. Even if the robot arm gets under the bent substrate 44, the substrate 44 will have residual static electric charge.
To prevent such problems, a separate static charge control process is typically performed after completing the deposition process. Specifically, the static charge control process includes injecting an inert gas, such as He, Ne or N2 gas, through a gas injection hole of the chamber, and then changing the injected inert gas into a plasma state by applying an RF power of about 400 W. The inert gas plasma neutralizes the static electric charge in the middle part of the substrate 44. The application time of the RF power is longer for larger amounts of more static electricity.
FIG. 2B is a cross-sectional view of a quantity of static electricity detected by the naked eye in the related art. To efficiently remove the static electricity generated between the upper part of the susceptor 50 and the substrate 44, the application time of the RF power to create the inert gas plasma should be adjusted in correspondence to the quantity of static electricity on the substrate. Various factors, such as environmental change within the chamber, can change the amount of static electricity generated. To this end, correct detection of the quantity of static electricity should be done so that an appropriate application time of the RF power to create the inert gas plasma can be determined. As shown in FIG. 2B, the effect of the static electricity is monitored by a naked eye 80 of a user through an external window 70 of the chamber 42 in the related art. That is to say, after completion of the deposition process, the application time of the RF power to create the inert gas plasma is controlled by a user who turned off the RF power, lower the susceptor 50 to deploy the lift pins 46 to see if the substrate 44 is no longer bent. If the substrate 44 is still bent, the susceptor 50 would be raised to undeploy the lift pins 46 and the substrate 44 would be resubjected to the inert gas plasma.
The related art apparatus and method for detecting the static electricity depends on user's judgment. Further, there may be still lingering static electricity that can cause problems when the substrate is moved after being determined as unbent. For example, a lingering static electricity can create significant attractive forces between the substrate and the robotic arm that can cause a damaging flex of the substrate during a subsequent release of the substrate by the robotic arm. In the related art, it is not possible to judge the generated quantity of static electricity, much less the residual amount of static electricity on the substrate. Thus, there is still a possibility that the substrate can be damaged by a residual static electric charge.